THE MASTERY OF THE AIR 247 
no wind against the bird and if the bird is not 
rising, the work of rowing with its wings in 
the elastic air is not hard. A ship has the 
advantage that it floats in the water, whereas 
the bird cannot float in the air; but the ship 
has the disadvantage that the water offers con- 
siderable resistance to a body passing through 
it, whereas the air offers little resistance to a 
smooth body passing quickly through it. 
The second kind of flight is gliding, seen 
when a bird, having got up a certain speed, 
rests on its oars, and holding its wings taut 
glides along, or when a bird launches itself 
from a tree and with outstretched, but un- 
moving wings, glides to the ground. When a 
bird glides along after getting up speed it is 
bound to sink, but this may be counteracted 
for a time if an ascending current of air beats 
up against the bird’s outstretched wings from 
below. We often see this when a gull flying 
from the fields seawards meets just above the 
edge of the cliffs an ascending landward 
breeze. In this case there is a transition to 
the third kind of flight, called “sailing.” 
SAILING FLIGHT.—When an albatross goes 
up one side of the ship, keeping pace with 
the vessel, without a stroke of its wings, we 
